Diniobioheteropoly acids and salts thereof



' 3,227,518 Patented Jan. 4, 1966 3,227,518 DINIOBIQHETEROPOLY ACIDS AND SALTS THEREOF John H. Kennedy, Santa Barbara, Calif., assignor to E. I.

du Pont de Nemours and Company, Wilmington, DeL,

a corporation of Delaware No Drawing. Filed Mar. 5, 1962, Ser. No. 177,212 16 Claims. (Cl. 23-50) This invention relates to a product and process, and more particularly, to a new class of mixed heteropoly acids and salts thereof and to a process for their preparation.

Heteropoly acids are complex inorganic acids containing two or more acidic atoms. This invention provides a new class of heteropoly acids which are acid-stable and organic-soluble, which have unique catalytic activity and which, in addition, can be used as corrosion inhibitors.

I-Ieteropoly acids of this invention are mixed heteropoly acids, that is, heteropoly acids containing, in addition to phosphorus, two or more diiferent kinds of acidic metal atoms, that is, polyelements. More specifically, the heteropoly acids of this invention are diniobioheteropoly acids containing, in addition to phosphorus and niobium, molybdenum or tungsten, or both molybdenum and tungsten.

The diniobioheteropoly acids of this invention and salts thereof have the formula:

and

being 5, x is a cardinal number of no greater than and nH O represents water of hydration. Usually n is up to 30, and most frequently on the order of about 3 to 20.

The products of this invention are prepared by bringing together, in an aqueous medium having a pH of about from O to 5, phosphate, niobate, and at least one of the group consist ng of para-molybda-te and para-tungstate. The tungstates and molybdates employed in the process of this invention are preferably compounds which are soluble in water such as, for example, the normal sodium, potassium and ammonium tungstates and molybdates, although compounds convertible to the soluble normal species also can be employed. The para-tungstate and para-molybdate solutions can be obtained from solutions of the normal compounds by treating solutions containing the norm-a1 species with acid (hydrogen ion) in the proportion of 1.5 moles of acid for each mole of the normal species present. Any strong acid such as hydrochloric acid, nitric acid, sulfuric acid, and the like, can be employed for this purpose. Instead of a separate pretreatment of the normal species, preferably, as illustrated in the examples, the para-tungstates and para-molybdates are formed in situ by employing sui'licient acid to convert the normal to the para species. Thus, for example, in the preparation of diniobiodecatungstophosphoric acid, normal-tungstate, ortho-phosphate and niobate can be contacted directly in aqueous medium at a pH of about 1. Phosphate can be supplied to the reaction mixture by any of the conventional ortho-phosphate-yielding substances such as phosphoric acid, alkali metal ortho-phosphates,

ammonium ortho-phosphates or mixtures thereof. The niobate contributing reactant is preferably a soluble alkali metal salt, although other water-soluble niobates also can be employed.

The concentrations of the reactants employed in the processes are preferably approximately stoichiometric quantities, the relative quantities of the tungsten and molybdenum reactants being computed on the basis of the proportions of tungsten and molybdenum desired in the final product. Excesses of either phosphate or niobate can be used in the reaction mixtures without detriment to product formation. Excesses of up to 100-fo1d of the phosphate are permissible, and even with large excesses of niobium only the diniobiophosphoric acids form, and the surplus niobium precipitates from the react-ion mixture.

The aggregation of the reactants to form heteropoly acids is pH dependent, and hence the most critical factor relating to the processes of the present invention is acidity. As indicated hereinbefore, the pH of the reaction mixture should be no greater than about 5. Acidity conditions optimum for the preparation of diniobiophosp-horic acids containing molybdenum occur Within the pH range 2 to 5, and preferably about 4. Optimum acidity for producing diniobiodecatungstophosphoric acid, containing no molybdenum, is within the pH range 0 to, 2, and preferably about 1.

Heating the reaction mixtures, although influencing the reaction rate, does not influence the reaction products. The reaction is conveniently carried out at reflux temperatures, about 100 C., and such temperatures are preferred. However, temperatures between about -150 C. and higher are operable in the process, if the application of such temperatures is desired. Lower temperatures can be used but are economically unsuitable. Higher temperatures may cause partial reduction to blue reduced heteropoly compositions or decomposition to the om'd-es, and hence are usually avoided.

The diniobioheteropoly acids are usually removed from the reaction mixtures by precipitation as insoluble salts or by extraction. If the former technique is employed, the free acids can be recovered by conventional ion exchange reactions. The latter technique employs an organic solvent in which the heteropoly acid is soluble. Suitable organic solvents in this connection include the polar organic solvents, and within this category, the oxygenated organic solvents are preferred. Such organic solvents as alcohols, ket ones, ethe-rs, carboxylic acid esters, phosphoric acid esters and the like are especially suitable, although one solvent may be more suitable for one diniobiophosphoric acid than for another.

The etliciency of theextraction step is influenced by the solvent employed and by the acidity of the heteropoly acid solution. For optimum results sufiicient hydrogen ion should be present to keep the heteropoly acids in solution in undissociated form. Since this is not always practical, that is, decomposition sometimes occurs in very strongly acidic media, molybdenum containing acids are extracted from solutions adjusted to about 0.1 to 1 N in'hydrogen ions, although higher acid concentrations are permissible providing that the contact times at the higher acidities are short. Diniobi-odecatungstophosphoric acid tolerates higher acid concentrations and is extracted from solutions adjusted to about 1-6 N in hydrogen ion. The particular solvent employed is chosen for its extraction efficiency within these acid ranges. Hence ethers, such as diethyl ether, are preferred for the extraction of dinio- 13 bio-decatungstophosphoric acids whereas alcohols, ketones, and esters, such as n-butyl alcohol, 3-pentanone, tributyl phosphate and the like, are especially suitable for the extraction of the molybdenum-containing diniobio-acids.

Recovery of the free heteropoly acids from the organic solvent solution is accomplished by evaporation of the solvent, usually, but not necessarily, under vacuum. Depending upon the conditions, the product can be obtained in a blue reduced form, which is easily converted to its original state by oxidation with such oxidizing agents as bromine water, nitric acid, etc.

The dini-obioheteroply acids of this invention obtained as described above have the general formula wherein x and nH O have the meanings noted hercinbefore. Illustrative of the acid products of this invention are diniobiodecatungstophosphoric acid, diniobiononatungstomonomolybdophosphoric acid, diniob-iooctatungstodimolybdophsphoric acid, diniobioheptatungstotrimolybdophosphoric acid, diniobiohexatungstotetramolybdophosphoric acid, diniobiopentatungstopentamolybdophosphoric acid, diniobiotetra-tungstohexamolybdophosphoric acid, diniobiotritungstoheptamolybdophosphoric acid, diniobioditungstooctamolybdophosphoric acid, diniobiomonotungstononamolybdophosphoric acid and diniobiodecamolybdophosphorie acid.

The salts of the heteropoly acids of this invention are obtained by replacement reactions, employing conventional techniques such as ion exchange, double decomposition, etc. The number of acid hydrogen atoms replaced is in part controlled by the ratio of salt cations to heteropoly anions in the mixtures and by the acid strength. However, the heteropoly acid salts of the larger cations as, for example, cesium, crystallize as acid salts under any conditions, probably because there is not enough room to accommodate all the large cations demanded by normal salt formation, that is, not enough room to permit replacement of all of the hydrogen atoms.

Illustrative salts obtained in accordance with this invention are the alkali metal salts such as sodium, potassium and cesium salts as well as ammonium thallium, barium, rubidium, silver, mercury, calcium, magnesium, strontium, cadmium and copper salts of the aforementioned heteropoly acids, for example, cesium diniobiodecatungstophosphate, thallium diniobiodecatungstophosphate, ammonium diniobiodecatungstophosphate, barium diniobiodecatungstophosphate, rubidium diniobiodecatungstophosphate, cesium diniobio-decamolybdophosphate, thallium diniobiodecamolybd-ophospha-te, cesium diniobiotetratungstohexamolybdophosphate, thallium diniobiote-tratungstohexamolybdophosphate, etc.

The dinio'biophosphoric acids are typical 12-heteropoly acids isomorphous with the l2-acids of the parent series containing only molybdenum and tungsten. The compounds are almost always highly hydrated, 20 or more water molecules not being unusual, and hydration often is essential to their stability. The free acids are soluble in water and in organic solvents. The molybdenum-containing acids are yellow in color, whereas those containing only tungsten and niobium are colorless. The diniobio-acids are strong oxidizing agents and can readily be changed to fairly stable reduced blue heteropoly compositions. The heteropoly anions are progressively degraded by hydroxide ion after neutralization and are completely decomposed by strong alkali.

The heteropoly acid and salt compositions of this invention are useful as catalysts, especially homogeneous catalysts, having the ability to dissolve in many organic solvents. For instance, the acid and salt compositions are very etiective dehydration catalysts. When a mixture of 20 ml. of cyclohexanol and g. :of the 12-diniobiodecatungstophosphoric acid are placed in a shaker bomb for one hour at 300 C., the product contains 78.2%

cyclohexene, 1.8% cyclohexanol, 14.8% cyclohexane and 0.7% cyclohexanone. When 5 g. of the ammonium salt of the heteropoly acid is substituted for the acid and the same conditions employed, the product contains 95.4% cyclohexene, 1.1% cyclohexanol, 1.8% cyclohexane and 1.6% cyclohexanone. The heteropoly compositions of this invention also catalyze the reaction of benzyl alcohol and benzoic acid to benzyl benzoate; the rearrangement of cyclohexanone oxime, in conjunction with polymerization to 6-ny-lon (heat to C.) the reaction of ethanol and acetal-dehyde to butadiene; and the dehydration of butanediol to tetrahydrofuran.

The din-iobioheteropoly acids and salts thereof of this invention are useful as corrosion inhibitors. For example, they can be used in retarding the corrosion of German silver, particularly in contact with detergents such as hot phosphate solutions. In this application they are particularly advantageous in that they are suitable in solutions Whose pH is as low as zero and are effective in organic systems such as Water-ethanol mixtures.

In the following additional and more detailed working examples, which illustrate this invention, parts and percentages are by weight unless otherwise indicated.

EXAMPLE I Preparation of diniobiodecatungslophosphoric acid A mixture containing 320 parts of aqueous 1 M sodium hydroxide solution, 480 parts of water, 320 parts of aqueous l M sodium tungstate solution and parts aqueous 1 M phosphoric acid solution is added to 320 parts of an aqueous solution containing 13.4 parts of sodium niobate (Na Nb O -9H O). The mixture is then acidified with 240 parts of aqueous 2 M sulfuric acid and boiled for 15 minutes. After cooling, an equal volume of concentrated hydrochloric acid is added, and the final solution is contacted with diethyl ether. Three layers form, the top containing ether, the middle aqueous waste and the bottom the other complex of the heteropoly acid. The etherate complex is separated from the waste, and the other is removed by evaporation at reduced pressures. The white solid product is found to have the following composition:

P O :2.45%; and H O=7.68%

indicating a tungsten-niobium mole ratio of 5 :1 and corresponding to the composition of diniobiodecatungstophosphoric acid, H PNb W O -9H O. Infra-red analysis confirms that the product is the aforementioned heteropoly acid.

To illustrate the effectiveness of the products of this invention as corrosion inhibitors, a strip of German silver, 21 non-ferrous alloy often called nickel silver containing copper, nickel and zinc, is immersed in various detergent solutions and heated at 75 C. for a period of time, then removed from the hot solutions and dried. Samples of German silver immersed in a 1% aqueous solution having a pH of 4 of alkyl aryl polyether alcohol, a conventional nonionic dispersing agent available as Triton X100, turn black and evidence substantial corrosion after immersion for one-half hour. Samples immersed in similar solutions containing 0.005%, 0.01% and 0.025% of the heteropoly acid of this example show markedly less corrosion, the samples immersed in the 0.025% solution being substantially similar to untreated samples. Similarly, improved corrosion resistance is obtained when the German silver is immersed in a solution containing 0.025 of the heteropoly acid and 1% of the aforementioned dispersing agent in an equal weight mixture of ethanol and water at a pH of 4, in solution containing 0.025% of the heteropoly acid and 1% of the aforementioned dispersing agent in water at a pH of 8, and in solution containing 0.025% of the heteropoly acid and 1% of sodium pyrophosphate at a pH of 8.

5 EXAMPLE H Preparation of diniobiodecamolybdophosphoric acid A solution containing 97 parts of sodium molybdate in 300 parts of water is acidified with 50 parts of concentrated hydrochloric acid. A solution containing 163 parts of sodium niobate (9-hydrate) in 400 parts of water is added, and a white precipitate forms. A solution containing 10.7 parts of disodium phosphate in 100 parts of water and then 15 parts of concentrated hydrochloric acid are added and the mixture is refluxed until essentially all the solid dissolves. Upon cooling, an equal volume of 1 M hydrochloric acid is added and the resulting solution is extracted with n-butyl alcohol. The organic layer is separated and evaporated to dryness at 100 C. under vacuum. The solid product is deep blue in color. The blue solid is then slurried with bromine water and heated at 100 C. under vacuum until dry. The product is a yellow solid, found by analysis to contain 68.8% M 11.6% Nb O 3.26% P 0 and 13.9% H O. The niobium-molybdenum mole ratio therein of 1:5 and infrared data indicates its structure to be that of the heteropoly acid, H PNb Mo O -13-6H O.

EXAMPLE III Preparation of diniobiotetratimgsohexamolybdophosphoric acid A solution of 61 parts of sodium molybdate in 175 parts of water is acidified with 62 parts of 6 M hydrochloric acid. An aqueous solution containing 82 parts of sodium tungstate, 175 parts of water and 62 parts of 6 M hydrochloric acid is added. To the resulting solution are added, in order, a solution containing 20.3 parts of sodium niobate (Q-hydrate) in 500 parts of water and a solution of 13.4 parts of sodium phosphate in 100 parts of water. The total mixture is then acidified with 300 parts of 6 M hydrochloric acid and refluxed for 7 hours. Upon cooling, an equal volume of 6 M hydrochloric acid is added and the mixture is extracted with ether. The ether layer is separated and evaporated to dryness, yielding 41 parts of a yellow solid. The compound contains 42.7% W0 35.4% M00 and 10.8% Nb O indicating a metal ratio of 2W:3M0:1Nb. This data together with the infrared spectrum of the product shows the product to be the heteropoly acid H5PNb2V4MO604Q' EXAMPLE IV Preparation of diniobiodecatangstophosphoric acid I To a soiution containing 82.5 parts of sodium tungstate in 400 parts of water, the following solutions are added, in order: 62 parts of 6 M hydrochloric acid, 9.4 parts of sodium niobate (9-hydrate) in 250 parts of water, 6.7 parts of disodium phosphate in 50 parts of water, and 10 parts of 6 M hydrochloric acid. The mixture thus obtained is refluxed overnight, and after cooling an equal volume of 6 M hydrochloric acid is added. The solution is then extracted with diethyl ether, and the ether layer is separated and evaporated to dryness under vacuum. The white compound obtained is identical in composition and structure to that prepared in Example I and has the formula: H PNb W O 91-1 0.

EXAMPLE V Preparation of diniobiodecatungstophosphoric acid The procedure of Example I is repeated except that a mixture containing 80 parts of 1 M sodium hydroxide, 200 parts of water, 80 parts of 1 M sodium tungstate, and 40 parts of 1 M phosphoric acid is added to a solution containing 6.3 parts of sodium niobate (9-hydrate) in water, and the mixture is acidified with 60 parts of 2 M sulfuric acid. A White product is recovered as described in Example I and identified as diniobiodecatungstophosphoric acid, H5PNb2W1oO4 9H20.

EXAMPLE VI Preparation 0) diniobiodecatangstophorphoric acid The procedure of Example I is repeated'except that a mixture containing parts of 1 M sodium hydroxide, 200 parts of water, 80 parts of l M sodium tungstate and 40 parts of 1 M phosphoric acid is added to a solution containing 3 parts of sodium niobate (9-hydrate) in water, and the mixture is acidified with 60 parts of 2 M sulfuric acid. A white product is recovered as described in Example I and identified as diniobiodecatungstophosphoric acid.

EXAMPLE VII Preparation of diniobiodecamolybdophosphoric acid The precedure of Example 11 is repeated except that to a solution containing 121 parts of sodium molybdate in 250 parts of water and 125 parts of 6 M hydrochloric acid are added, in order: 9.4 parts sodium niobate (9- hydrate) in 250 parts of water, 13.4 parts of disoduim phosphate in parts of water, and 15 parts of 6 M hydrochloric acid. The yellow product obtained is identified as diniobiodecamolybdophosphoric acid, identical to that obtained in Example II.

EXAMPLE VIII Preparation 07 cesium diniobiodecatungstophosphate EXAMPLE IX Preparation of thallium diniobiodecatungstophosphate The procedure of Example VIII is followed except that a solution containing 5.00 parts of thallous sulfate replaces the cesium chloride solution. The thallium salt, Tl H PNb W O -18H O, is obtained as a white insoluble solid. The product is found to have the following composition: 58.8% W0 7.0% Nb O 2.0% P 0 19.6% T1 0, 8.5% H 0.

EXAMPLE X Preparation of ammonium diniobiodecatungstophosphate The ammonium salts of diniobiodecatungstophosphoric acid is prepared by following the procedure of Example VIII, except that 100 parts of 1 M ammonium chloride, is substituted for the cesium salt solution. The ammonium salt corresponds to the formula 3H2PN1J2W10040 EXAMPLES XI-XII Preparation of barium and rubidium diniobiodecatungstophosphates The barium and ubidium salts of diniobiodecatungstophosphoric acid are prepared following the procedure of Example VIII, except that 3 parts of the heteropoly acid in 100 parts of hydrochloric acid are treated with 5 parts of barium chloride or 5 parts of rubidium chloride, re-

spectively, in 100 parts of water. The colorless, insoluble salts obtained correspond to the formulae:

BZlHgPNbzWloOag' rlHgO and Rb l-I PNb V/ O "I120 EXAMPLE XIII Preparation of cesium diniobiodecamolybdoplzosphate To a solution containing 3 parts of diniobiodccamoylbdophosphoric acid dissovled in a minimum of 0.1 M sulfuric acid is added 10 parts of cesium chloride in 500 parts of water. The mixture is cooled in ice and filtered, and the solid product is washed with ice water, alcohol and finally with ether. Anaylses indicate the yellow cesium salt to correspond to the composition represented by the formula, Cs H PNb Mo O 'nl-I O. The product is found to have the following composition: 57.5% M 3 9.3% Nb O 2.91% P 0 6.50% H O; 24.3% C5 6.

EXAMPLE XIV Preparation of thallium diniobiodccamolybdop/sosphatc The procedure of Example XIII is followed except that 500 parts of 0.1 M thallous sulfate is substituted for the cesium salt solution. The composition of the yellow product corresponds to the thallium salt,

The product is found to have the following composition: 50.9% M00 8.4% Nb O 3.10% P 0 5.64% E 0; 26.3% T1 0.

EXAMPLE XV Preparation of cesium dini0biotetratungstolzcxamolybdophosphate The procedure of Example XIII is followed except that 3 parts of diniobiotetratungstohexamolybdophosphoric acid is substituted for the diniobiodecamolybdophospihoric acid. The cesium salt is pale yellow in color and corresponds to the formula Preparation of tallium dini0biotatratungstohexam'olybdophosp hate The procedure of Example XV is followed except that the cesium chloride solution is replaced by 500 parts of 0.1 M thallous sulfate. The yellow insoluble thallium salt corresponds to the formula,

Preparation 0 dim'obiodecatimgstophosphoric acid Sodium potassium niobate (39 parts) is dissolved in 1000 parts of boiling water. A solution of 304 parts of sodium tungstate dihydrate in 500 parts of Water is added, followed by 119 parts of sodium hydroxide and 110 parts of 2 M phosphoric acid. From a dropping funnel is added slowly 9 M sulfuric acid unitl pH 4 is reached. Then 224 parts of l M sulfuric acid is added and the solution is boiled for minutes. Upon cooling, 2380 parts of concentrated hydrochloric acid is added and the acidic solution is extracted twice with ether. The etherate layer is removed and dried by evaporation at reduced pressures. The compound is identical to that obtained in Example 1.

Sodium potassium niobate is prepared by dissolving 2 parts of sodium niobate in 100 parts of water and adding hot to 300 parts of a hot equimolar sodium hydroxidepotassium hydroxide mixture, 5 M in hydroxide concentra tion. The solution is cooled quickly to ice temperature and the product is removed by titration. The solid is washed with ice water and with boiling ethanol and dried.

8 EXAMPLE XVIII Preparation of ammonium diniobiodecamolybdophosphate A solution is prepared from 194 parts of sodium molybdate dihydrate and 306 parts of water. Concentrated hydrochloric acid (112 parts) is added slowly from a dropping funnel. A cooled solution prepared from 34.4 parts of sodium potassium niobate in 800 parts of hot water is then added, and with mixing is added a solution of 21.4 parts of disodium hydrogen phosphate in 260 parts of water. After the addition of 33.6 parts of concentrated hydrochloric acid, the mixture is refluxed for minutes. The mixture is then cooled in ice, an equal volume of l M hydrochloric acid is added and the acidic mixture is extracted five times with 454 parts of n-butariol. Each ofthe butanol layers is leached with water, and. the extracts are adjusted to pH 4.2 with ammonium hydroxide. The combined extracts are then evaporated to a small volume by heat and the resulting mass is dried by heating at 8090 C. at reduced pressures. The compound is found by analysis to contain 61.5% M09 12.5% Nb O 3.39% P 0 15.60% H O; 6.9% (NHQ O, corresponding to the formula:

Preparation of ammonium diniobiodccamo-lybdophosphate Following the procedure of Example XVIII except that the product is dried by heating at C. at reduced pressures, a product whose composition corresponds to the formula (N lgl-l PNb lvfo O -161-1 0 is obtained. By analysis, the compound is found to contain 64.3% M00 13.4% Nb O 3.79% P 0 13.85% H 0; and 1.3% (NHQ O.

I claim:

1. A compound having the formula:

wherein y is a cardinal number of no greater than 5, M is an inorganic cation selected from the group consisting of alkali metals, ammonium and thallium whose valence is z, the sum of y and being 5, x is a cardinal number of no greater than 10 and nH O represents Water of hydration and n is no greater than 30.

2. A heteropoly acid of claim 1 having the formula:

. A heteropoly acid of claim 2 wherein at is zero. A heteropoly acid of claim 2 wherein x is 10.

. A heteropoly acid of claim 2 wherein x is 4.

An inorganic salt selected from the group consisting of alkali metals, ammonium and thallium salt of a heteropoly acid of claim 2:.

7. An alkali metal salt of a heteropoly acid of claim 2.

3. A process for producing diniobioheteropoly acids and salts thereof which comprises bringing together, in an aqueous solution having a pH of about from zero to 5, Water-soluble phosphate ions, niobate ions and at least one of the group consisting of para-molybdate and paratungstate ions at a temperature from about 50 C. to 156 C.

9. The process of claim 8 wherein at least one or" the group consisting of normal-tungstate and normalmolybdate is charged to the reaction mixture and converted in situ to the para species by adding at least 1.5 moles of hydrogen ion for each mole of said normaltungstate and molybdate.

9 v 10 10. The process of claim '8 wherein the source of 13. The compound of claim 2 wherein n is from 3 phosphate is phosphoric acid, the source of niobate is to 20. sodium niobate, the source of molybdate is sodium molyb- 14. H PNb W O -9H Q date and the source of tungstate is sodium tungstate. 15. H PNb Mo O -13.-6H O. 11. The process of claim 10 wherein the ratios of phos- 5 16. H PNb W Mo O -18H O. phate, niobate, molybdate and tung-state are about References Cited by the Examiner stoichiometric with the proportions of phosphorus, niobium, molybdenum and tungsten desired in the final UNITED STATES PATENTS product 2,608,534 8/ 1952 Fleck 252-435 12. The compound of claim 1 wherein n is from 3 10 2744928 5/1956 Smith at 252435 X to 20. MAURICE A. BRINDISI, Primary Examiner. 

1. A COMPOUND HAVING THE FORMULA: (H)Y(M+Z)((5-Y)/Z)P(NB)2(W)X(MO)(10-X)(O)40 . N(H2O) WHEREIN Y IS A CARDINAL NUMBER OF NO GREATER THAN 5, M IS AN INORGANIC CATION SELECTED FROM THE GROUP CONSISTING OF ALKALI METALS, AMMONIUM AND THALLIUM WHOSE VALENCE IS Z, THE SUM OF Y AND (5-Y)/Z BEING 5, X IS A CARDINAL NUMBER OF NO GREATER THAN 10 AND NH2O REPRESENTS WATER OF HYDRATION AND N IS NO GREATER THAN
 30. 2. A HETEROPOLY ACID OF CLAIM 1 HAVING THE FORMULA:
 6. AN INORGANIC SALT SELECTED FROM THE GROUP CONSISTING OF ALKALI METALS, AMMONIUM AND THALIUM SALT OF A HETEROPOLY ACID OF CLAIM
 2. 8. A PROCESS FOR PRODUCING DINIOBIOHETEROPOLY ACIDS AND SALTS THEREOF WHICH COMPRISES BRINGING TOGETHER, IN AN AQUEOUS SOLUTION HAVING A PH OF ABOUT FROM ZERO TO 5, WATER-SOLUBLE PHOSPHATE IONS, NIOBATE IONS AND AT LEAST ONE OF THE GROUP CONSISTING OF PARA-MOLYBDATE AND PARATUNGSTATE IONS AT A TEMPERATURE FROM ABOUT 50*C. TO 150*C. 